An annual report by the Czech counter-intelligence agency, BIS, states that a large number of Russian intelligence officers are currently working “under diplomatic cover,” with local media stating that although this is well-known, it is quite difficult to expel such spies.

The Czech daily Lidove Noviny noted that while the Russian embassy dwarfs other embassies in terms of personnel—and while many employees in the embassy are spies—the process of expelling embassy works or diplomats only results in a tit-for-tat reaction in Russia.

The paper added that sources now claim that up to two-thirds of diplomatic staff are actually spies.